Expendable sonobuoys and related monitoring devices typically are the victims of long periods of storage. After a long-shelf time, it is not uncommon for the sonobuoy sensors and the electronics to deteriorate or otherwise fail. Changes in acoustic or electronic sensitivities can reduce their effectiveness for data gathering or detection purposes. Technicians usually perform routine testing and maintenance at predetermined intervals. Test equipment is plugged into modules on the units and readings representative of the spectral distributions and amplitudes of signals of interest are observed. While this inspection procedure reveals some equipments' failures, it cannot indicate if components have become defective in the period between the last inspection and the actual use of a sonobuoy unit. Most assuredly, this calibration technique cannot detect faulty components in a sonobuoy after it has been deployed and is gathering data. Thus, there is a continuing need in the state-of-the-art for a calibration unit which is compact and highly reliable to allow its inclusion with expendable sonobuoys to allow the calibration thereof for and during deployment.